1. Field of Invention
This invention relates generally to underground storage of gases and liquids and, more particularly, to an engineered, scalable system and method for containment of gases and liquids both in virgin rock formations and in formations that have previously been drilled and/or used for storage.
2. Related Art
This invention relates generally to underground storage of gases and liquids and, more particularly, to an engineered, scalable system and method for containment of gases and liquids both in suitable rock formations and in formations that have previously been drilled and/or used for storage.
Heretofore, the underground reservoirs typically used for such storage have included old salt or limestone mines, solution mined salt domes, depleted gas or oil fields, saline aquifers, and other underground sites having geological features that make them suitable for gas storage. A major disadvantage is that reservoirs of this nature can only be used where they are found. They cannot be positioned where storage is needed, and they cannot be scaled to meet the performance needs and other requirements of a particular application.
The natural gas industry has stored natural gas in reservoirs for many years. A network of storage facilities supports the U.S. natural gas distribution network. These reservoirs are generally of three types: depleted oil or gas fields, solution mined or pre-existing mined out salt domes and saline aquifers. According to the Federal Energy Regulatory Commission (FERC), 86% of underground storage capacity today is in depleted reservoirs. Depleted reservoirs are a powerful analog for the invention described herein. The gas storage industry has recently focused on developing storage in salt caverns. While still less that 5% of total gas storage in the U.S., salt caverns have the distinct advantage of enabling relatively rapid injection and withdrawal of gas to meet increasing needs of distributers and commercial users for mechanisms to manage their supply chain in the context of very high price volatility. Major disadvantages of the present natural gas storage models include: 1) depleted reservoirs generally are not designed to enable rapid injection and withdrawal of gas, 2) there is a limited number of salt domes or saline aquifers and these are not located heterogeneously throughout the country, 3) access to these sources is limited to their license holders, and 4) leakage has been a problem in the natural gas storage industry.
Compressed air energy storage (CAES) is a proven and effective way to store electrical energy generated during periods of relatively light demand and/or by alternative energy sources such as solar, wind, and nuclear sources for use during periods of greater demand. In such systems, compressors convert electric power to compressed air which is stored in a reservoir, and then when the power is needed, the compressed air is recovered from the reservoir converted back to electrical energy by compressed air turbine driven electrical generators. While (CAES) has been a proven technology and applied for over twenty years, to date, for a variety of reasons, (CAES) has been somewhat limited in its application. Many researchers project a dramatic increase in (CAES) due to the growth of alternative energy production, wind and solar energy, as the U.S. attempts to wean itself from fossil fuel sources of electrical energy. If (CAES) is to meet the needs of the alternative energy industry, a major limiting factor is likely to be the difficulty in locating acceptable reservoirs.
There has been significant investment in injecting CO2 in active oil fields to produce additional oil—this is known as Enhanced Oil Recovery or EOR. CO2 is produced currently from naturally occurring reservoirs and shipped by pipeline to the oil field. Major companies are in the business of extracting and shipping this CO2 for sale to the oil producers. The U.S. Department of Energy is investing significant amounts of money in assessing the efficacy of sequestering CO2 in active or depleted oil and gas fields, but the extent to which CO2 can be sequestered in such fields is probably limited by the fact that oil and gas fields often leak even when they are plugged and abandoned. Effective sequestration requires that CO2 be permanently stored in secure reservoirs that can be monitored and audited. The U.S. Department of Energy is investing significantly in a program to determine the best methods for permanent storage of CO2 in geologic reservoirs. However, the D.O.E. program concentrates on locating reservoirs with natural pre-conditions that are acceptable for this purpose. Four significant disadvantages exist in the present CO2 sequestration models being investigated: 1) EOR does not secure CO2 storage reliably, 2) natural reservoirs are difficult to discover, qualify and to get clear ownership of, 3) most natural reservoirs and oil and gas fields leak, 4) saline water in natural reservoirs can interact with the substance being stored, and 5) natural reservoirs and oil and gas fields can be a very long distance from the sources of the captured CO2.